also sub-station, 1864 in the policing sense, from sub- + station (n.). Power grid sense is attested from 1889.
Entries linking to substation
sub-
word-forming element meaning "under, beneath; behind; from under; resulting from further division," from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough"), from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo "under," also "up from under." The Latin word also was used as a prefix and in various combinations.
In Latin assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-. In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.
The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontractor); "inferior" (17c., as in subhuman); "smaller" (18c.); "a part or division of" (c. 1800, as in subcontinent).
station n.
late 13c., "place which one normally occupies," from Old French stacion, estacion "site, location; station of the Cross; stop, standstill," from Latin stationem (nominative statio) "a standing, standing firm; a post, job, position; military post; a watch, guard, sentinel; anchorage, port" (related to stare "to stand"), from PIE *steti-, suffixed form of root *sta- "to stand, make or be firm."
Meaning "each of a number of holy places visited in succession by pilgrims" is from late 14c., as in Station of the Cross (1550s). Meaning "fixed uniform distance in surveying" is from 1570s. Sense of "status, rank" is from c. 1600. Meaning "military post" in English is from c. 1600. The meaning "place where people are stationed for some special purpose" (as in polling station) is first recorded 1823. Radio station is from 1912; station break, pause in broadcasting to give the local station a chance to identify itself, is from 1942.
The meaning "regular stopping place" is first recorded 1797, in reference to coach routes; applied to railroads 1830. Station-master is from 1836. Station wagon in the automobile sense is first recorded 1929, from earlier use for a horse-drawn conveyance that took passengers to and from railroad stations (1894). Station house "police station" is attested from 1836.